An input of a circuit may for example be derived from an analog sensor signal. The analog sensor may indicate the occurrence of an event, for example, that a current has crossed a threshold. The occurrence of the event may be stored in a memory element and may be further processed afterwards. Such a circuit may be called an event catcher.
However, the shape and the timing of the signal at the input of the circuit may be uncertain. It is therefore possible that the timing conditions such as the setup time, hold time, minimum pulse width, etc. of the memory element may be violated and that the occurrence of an event is not recorded properly.
If the timing conditions of a memory element are violated it may stay in a metastable state for an uncertain time before it will toggle into one of its stable states. The stable state into which the memory element will toggle is also unpredictable. A metastable state may propagate to other parts of the circuit and may result in undefined behavior. As an example, this may occur in mixed-signal processing, where outputs of analog components are processed by a clocked digital logic and where the control logic of the analog components is not synchronized with the signal clock of the digital logic.